1. Field of the Invention
The present invention relates to a radio communication apparatus, method and program, and more particularly, a radio communication apparatus using the Space Division Multiple Access (SDMA) scheme.
2. Description of the Related Art
Space Division Multiple Access (SDMA) is known as a multiplexing technique that enables a plurality of radio terminals to transmit data of the same frequency to a radio base station at the same point of time, thereby enhancing the efficiency of transmission. Further, there is a simple method using a polling algorithm and employed by a radio base station, the method being used to impart permission of SDMA transmission to each radio terminal (see, for example, Japanese Patent No. 3822530). In this method, each radio terminal stochastically acquires a right of access to the base station upon receiving a reported polling signal, thereby enabling simultaneous access to the base station using SDMA and suppressing, within a maximum spatial multiple number, the number of radio terminals that simultaneously access the base station (i.e., an access count).
However, in the technique disclosed in Japanese Patent No. 3822530, whenever a reported polling signal is received, a right of access is intended to be acquired with the same probability. Therefore, the right of access may not always be obtained. Although the probability of acquisition of the access right becomes stochastically equal as the number of trials of access by each terminal increases, differences may well occur in the number of acquisition times of the access right in the short term.